Broad band vertical antenna with adjustable impedance matching network



Aug. 13, 1963' H. BRUECKMANN 3 00,8

BROAD BAND VERTICAL ANTENNA WITH ADJUSTABLE IMPEDANCE I MATCHING NETWORKFi led Nov. 50. 1960 FIG. 2B

FIG.2A I

UTILIZATION DEVICE United States Patent M (Granted under Title 35, US.Code (1952), see. 266) l The invention described herein may bemanufactured and used by or for the Government for governmentalpurposes, without payment of any royalty thereon.

The present invention relates to an improved broadband verticalantennaand more particularly to one for vehicular application constructed inthe form of a whip and employing a double feed system, facilitating itsuse over a broad band of frequencies.

In the prior art, whip antennas for vehicular use required complicatedcircuitry and were not conveniently adjhstabio for operation over a widefrequency range. The present invention is a vertical Whip antenna(operating, for example, over the frequency range from 20 to 76 me.)

which will permit considerable simplification of the an' tenna circuitryof vehicular radio sets,-especially with respectto simplification of thematching circuitry of the radio sets, and which will also permit anincrease, inantenna efliciency.

The present invention is an improvement over my Patent No. 2,913,722,The antenna system described therein comprises an antenna having upperand lower sections, a cable choke connected to the .base'of the lowersection, 'reactance'circuits, and switching means for con- I nec'tingthe reactance circuits to the upper and lower sec- 5 tions. Theinvention herein provides improvements over the above-mentionedpatent-by having the cable choke wound around a ferrite core to reducethe turns required, and -by havinga tapped shunt coil connected acrossthe cable choke to minimize the ferrite'losses at high frequencies. Inaddition, the-upper section has now been changed to provide a dualfunction. While it, still behaves as an upper radiator, it also actsjasan impedance matching stub, being either open-ended or shorted,depending on the load impedance. This, latter structural change resultsin the voltage standing wave ratio (VSWR) of the antenna being.-reduced. Another means for reducing the VSWR isthe introduction of ataper in the lower section so that a portion thereof will have arelatively high characteristic impedance, the remainder of the lowersection having a somewhat lower characteristic impedance. Q 1 I jPrincipal Advantages 1) The proven mechanical advantages of the whipconfigurationare not compromised. Theneare no moving parts, telescopingsections, or lumped reactors in'the .whip

A itself. I

(2) v The length of the cable ,choke is kept to a'm-inh mum -by havingit wrapped around a ferrite core. I A tapped shunt coil is connected inparallel with thev cable choke todecrease the inductance as thefrequency is invariable lumped-reactor comprising the cable choke woundon the ferrite core, the tapped coil shuntingthe choke, the impedancematching networks, and the switch: ing means; By switching to the properimpedance matching network and to the proper tap .on the tappedcoil, by

means of anautomatic" remote control activated the 3 ,190,893 PatentedAug. 13, 1963 2. frequency dial of the utilization device, the frequencyrange is divided into anumber of fairly wide bands, each band having theproper reactance value. This permits controlling the currentdistribution along the lower section of the antenna below the feed pointwithin wide limits so that a current node is placed'at or near the lowerend of the lower section in all bands. As a result, the distortion ofthe azimuth pattern and the losscaused by unintentional excitation ofthe vehicle body are minimized. Most important, the decoupling betweenantenna and vehicle body actually achieved is sufiicient' to makedifferences in impedance due to vehicle type, mounting location andground conditions negligibly small. As a secondary effect, the powergain with respect to the field strength on the ground is improvednoticeably at the upper end of the frequency range. In addition, thefeed cable from the antenna to the utilization device can be anyarbitrary length, no tuning is involved, and the voltage standing waveratio (VSWR) is kept small over the entire frequency range. I

(4-) To reduce the VSWRin adjoining sections of the antenna, over theentire frequency range, the upper section of the antenna is constructedso that its acts as a radiator and stub simultaneously, and the lowersection of the antenna is construoted with a tapered portion. Thetapering of the lower section has an additional advantage of equalizingthe antenna impedance seen at the lower end of the cable choke and thecharacteristic impedance of the transmission line connected to theutilization device.

The advantages of lower V SWR are lower line loss, and lower voltageacross the transmission line and other components, (less danger ofvoltage breakdown). Also, lower VSWR permits use of simpler, less lossymatching networks. The' same, advantage accrues from equalizing theimpedance seen at the lower end of the cable choke and thecharacteristics impedance of the transmission line connected to theutilization device, which may be a transmitter or a receiver.

other advantages will bereadily apparent from consideration of thefollowing specification relating to the annexed drawings in which:

and

FIGURES 2A and 2B are enlarged views of alternative connections of theupper radiator (stub) to the lower radiator.

Although the antennamay beused with either receiving or transmittingequipment, it will be referred to, for convenience, as a radiator, asfora transmitter. Therefore, the termsupper radiator andlower radiator areused throughout the specification andclaims as generic to bothtransmitting and receiving' antennas. The terms section and radiatorapplied to the antenna elements, as upper section or upper radiator 12,are equivalent." Also, the term utilization device, asused herein, is tobe considered 1 FIGURE 1 is a schematic illustration of the invention;

' generic to t'ransmitter's and receivers.

Referring now to the drawings, wher'einlik-e reference charactersdesignate like or corresponding parts through out the several views,there is shown intFlGU R 'E 1, an

"irnproved double feed whip antennasystem cc'mipri-sing an upper section(upper-radiator), 12"landflower-jsection (lower radiator) 13, the twosections'lz and 13 being I inclosed within an insulating jacket. 14, QIn a preferred emhodimentthe antenna is l22 in ches in length with theupper radiator IZ-beingapproximately 69 inches and gthe lower radiator13 being approximately 53 inches. Insu lating jacket d4 servestosupport; and stiffen the coaxial Spring 45 and base insulator 49, eachcoaxial with lower section 13 at its bottom end' are positioned outsideof and adjacent to insulating jacket 14, as shown, and act as the basesupport for the antenna. Base insulator 49 is attached to vehiclebcdymember 48 where the lower section 13 passes through that member toconnect to cable choke 17.

A shield housing 52 is mounted within vehicle body member 48 about baseinsulator 49-. Encased within this housing'is ferrite-cored cable cholce17, tapped shunt coil 60 (shunting the cable choke), impedance matchingnetworks, and ganged switching network 20.

Ganged switching network 20*, remotely controlled firom the radio set orother utilization device 61, and activated automatically from abandselector (not shown), is illustrated as comprising five ganged switches23, 24, 25", 26 and 27--each having a switch arm and three switchpositions I, II and III. This switch permits changing the impedance ofthe network (matching networks 36, 39 and 41, cable choke 17, and tappedshunt coil 60) coupling the antenna to utilization device 61 byinnerconductor 43 of coaxial cable 44, as described more 'fully in my PatentNo. 2,91 3,7 22.

While'each deck ott ganged switching'network 20 is shown having threepositions for covering the entire firequency range, a greater number orsuch positions and impedance matching networks may be used. Tapped shuntcoil 60' will accordingly have an additional number of taps.

The lumped reactor at the base of lower radiator 13 has, an essentialcomponent, a section of coaxial cable wound on ferrite core 59 to formcable choke 17, the

(ferrite core being used to keep the number of turns of the cable choketo a minimum.

For the purpose of illustration, cable choke 17 is shown as having oneturn in FIGURE 1. Actually, however, it will have a plurality of turns.Because of the ferrite core the preferred embodiment needs only four theldifiiculty of matching at the lower end of the fre quency range.

Upper section -12 of the antenna comprises a coaxial line having outerconductor 12a and inner conductor 12b. This line acts as aradiator forcurrents flowing on the outside of outer conductor 12a, and as a stubfor currents flowing on the inside of outer conductor 12a and in innerconductor 12b (currents in 12b are always equal in magnitude andopposite in direction to those on the inside of outer conductor 12a).The arrows in FIG- URES 2A and 2B show the current flow for aseriesconnected stub and parallel-connected stud, respectively. Thedashed capacitors in these figures depict the capacitance between thecable portions closing the antenna circuit.

When inner conductor 12b is shorted to outer conductor 12a (FIGURE 23),the line acts asa shorted stub. With this type of termination, thecenter conductor 12b is usually connected in parallel with the feedpointimpedance of the antenna (see FIGURE 2B) although in narrow-bandapplications the series connection might be employed to advantage.

Upper radiator '12 may alsobe open-ended, as in FIG- URE 2A, wherein thelength of the inner conductor is the; length of the stub and the lengthof the outer conductor is equalto or greater than the stub length. Inthis arrangement upper radiator 12 is connected usually in series willlower radiator 13.

The embodiments shown in FIGURES 2A and 2B are not equivalent, but arecomplementary. The series conmotion of the stub (usually resonant in themiddle ofthe frequency range) is most effective with respect tobroadband compensation when the load impedance (in this case the steedpoint impedance) is high. On the other hand, the parallel connection isuseful when the load impedance is low.

Lower section 13" is formed oftwo transmission lines 1 63 and 640idifferent diameter and characteristic. im-

and' one-hali turns or cable (twenty-three inches of cabie I length) to[obtain an inductance ost 2' wh. The ferrite core'in this embodiment isa cylinder 1.0 inch in diameter and 2.0 inches long. p

Connector 62 couples one end of cable choke 17 to the base ocflowerradiator 13. If desired, the cable choke can be formed. integral withthe lower radiator. At the other end of the cable choke the innerconductor is connected toswitching network 20, and the outer-conductoris grounded to housing 52 which shields network 20' I Tapped shunt coil60, a cylindrical air-core coil, with relatively loose coupling betweenturns, is connected in parallel with cable choke. -17. The taps are eachconnected to a switch terminal of switch. deck 24 to permit adjustmentof the coil, acconding to the switch position, to tune theselfcapacitance of the cable choke and the capacity of the baseinsulator-and other associated hardware to enhance the broad-bandproperties of the antenna. Adjustment ofthe inductance value of thiscoil, by the use of the taps,'is preferable to an adjustment of thecable cholce, particularly in the; higher frequency range to minimizethe ferrite-losses or core 59. As the frequency is increased theinductance of the shunt coil is lowered pedance. The lower end of 63 istapered to match the smaller diameter of 64, as shown in :FIG. 1.

The tapering of the line made up of 63 and 64 has the effect ofequalizing the antenna impedance seen at 35 to that of thecharacteristic impedance of coaxial cable 44. Any tapering, [gradual orinstep's, can be done. to the inner conductor alone, to the routerconductor alone, or to both. v

The stub 12 and the tapered section made up of 63 and 64 can be usedeither together or' independently of each other to reduce the VSWR'oye-rthe entire frequency range. The advantages of lower VSWR are lowerline-loss and lower uoltage (less dan'ger of voltage breakdown). Also,low VSWR permits the use. of simple,

It should be understood, of course, that the foregoing disclosurerelates to only a'preferred'embodiment of the I invention and thatnumerous: modifications or alterations may be made therein withoutdeparting from the spirit and scope of the invention as set torth theappended due to the capacity of the base assembly flowsthrouigh I itrather than through. the cable choke. As, a result thelosses in thebasereactor assembly, using a ferrite core 7 such as that, commonly known.as Q.-2,' do not exceed 5% of the antenna inputpower.

The. criterion used in, adjusting the taps \ot the shunt A p coil isprimarily' the position of the node of the current "distribution alongthe antenna. Specifically, positioning thenode at the base minimizes itscoupling to the vehicle body, whereas positioning. the (virtuallcurrentnode below thebase of the antenna, corresponding to acapacitivesusceptanc'e o f'the. base reactor, greatly alleviates claims.

What is claimed is:

1. An improved broad-band whip antenna for vehic'u- V 7 larusecomprising: an antenna having an uppersection and a lower sectionelectrically coupled tosaidupper section; a' fer-rite core; a cablechoke wound around said ferrite-core; means for connectingsaid lowersection to said cable choke; a tapped shunt coil connected in parallelwith said cable choke and having a plurality of taps; a plurality ofimpedance matching networks; and switching means for connecting any oneof said impedance matching networks to said antenna and for changing theinductance of said shunt coil by the tap setting according to thefrequency band at which the antenna is to operate.

. 2. The improved broad-band'vvhip antenna of claim 1 wherein said lowersection is formed of two coaxial lines, one line having a lowercharacteristic impedance lower section, respectively.

4. The improved broad-band whip antenna of claim 3 wherein said uppersection is formed of a coaxial line having the upper extremity of theinner conductor insulated from the outer conductor and the lowerextremity of the inner conductor connected to said inner conductor ofsaid lower section.

5. The improved broad-band whip antenna of claim 3 'wherein said uppersection is formed of a coaxial line withthe inner conductor connectedto-the outer conductor of said lower section and the outer conductorconnected to the inner conductor of said lower section.

6. An antenna system for vehicular use comprising: an antenna insulatedfrom and projecting outwardly from the structure of the vehicle so as tobe electrically exposed to space, said antenna having upper and lowersections; an insulating jacket encasing said antenna; a ferrite core; acable choke wound around said ferrite core and connected to the lowerextremity of said lower section; a tapped shunt coil having a pluralityof taps and its extremities connected in parallel with said cable choke;a plurality of impedance matching networks; a switching means forinterconnecting said impedance matching networks to said antenna and forchanging the tap connections on said tapped shunt coil.

7. An improved broad-band whip antenna system for vehicular usecomprising: an nppersection formed of a coaxial line; a lower sectionhaving an upper and lower portion, each portion being formed of acoaxial line, the lower end of said upper portion being tapered andbuttconnected to the upper end of said lower portion; section'connection means for connecting said lower section to said uppersection; an insulating jacket encasing said upper and lower sections; aferrite core; a cable choke of coaxial cable wound around said ferritecore; means for connecting said cable choke to said lower section; atapped V shunting coil having a plurality of taps, said shunting coilconnected in parallel with said cable choke across the outer conductorof said coaxial cable forming said cable choke; a plurality of impedancematching networks; a'

ductance of said shunt coil by the tap setting according to thefrequency band at which the antenna is to operate.-

8. An improved broad-band whip antenna system for vehicular usecomprising: an upper radiating section formed of a coaxial line; a lowerradiating section having an upper and a lower portion, each portionbeing formedlof a coaxial line, said upper portion having a highercharacteristic impedance than said lower portion, said upper portionhaving its lowest extremity tapered, said lower portion having its upperextremity connected to said tapered extremity of said portion; sectionconnection means for connecting said upper section to said lowersection; an insulating jacketencasing and supporting said upper andlower sections; a ferrite core; a cable choke of a coaxial cable woundaround said ferrite core; a switching means; means for connecting theinner and outer conductors of one end of said cable choke to the innerand outer conductor,respectively, of said lower portion of said lowersection, the inner and outer conductors of the other end of said cablechoke being connected to said switching means and ground, respectively,said outer conductor of said one end of said cable choke being connectedto said switching means; a tapped shunt coil having a plurality of tapsand connected to the outer conductor of said.

cable choke in parallel therewith, said taps being connected to saidswitching means; a utilization device; and means for connecting saidutilization device to said switching means; whereby said switching meansconnects one of said plurality of impedance matching networks between.

said antenna and said utilization device and changes the inductance ofsaid shunt coil by the tap setting according to the frequency band atwhich the antenna will operate.

9. The improved broad-band whip antenna "system of claim 8 wherein theinner conductor of said upper section is connected to the outerconductor of said lower section and said outer conductor of said uppersection is connected to said inner conductor of said lower section toform said section connection means, so that said upper section acts as aradiator and parallel connected stub simultaneously.

10. The improved broad-band whip antenna system of claim 8 wherein thelower extremity of the inner conductor of'said upper section isconnected directly to the inner conductor of said lower section to formsaid section connection means, so that said upper section acts asaradiator and a series-connected stub simultaneously.

References Cited in the file of this patent UNITED STATES PATENTS2,658,145 Dorne et al Nov. 3, 1953 2,748,386 Polydoroif May 29, 19562,913,722 Bruechmann Nov. 17, 1959 2,991,355 Spindler July 4, 1961

6. AN ANTENNA SYSTEM FOR VEHICULAR USE COMPRISING: AN ANTENNA INSULATEDFROM AND PROJECTING OUTWARDLY FROM THE STRUCTURE OF THE VEHICLE SO AS TOBE ELECTRICALLY EXPOSED TO SPACE, SAID ANTENNA HAVING UPPER AND LOWERSECTIONS; AN INSULATING JACKET ENCASING SAID ANTENNA; A FERRITE CORE; ACABLE CHOKE WOUND AROUND SAID FERRITE CORE AND CONNECTED TO THE LOWEREXTREMITY OF SAID LOWER SECTION; A TAPPED SHUNT COIL HAVING A PLURALITYOF TAPS AND ITS EXTREMITIES CONNECTED IN PARALLEL WITH SAID CABLE CHOKE;A PLURALITY OF IMPEDANCE MATCHING NETWORKS; A SWITCHING MEANS FORINTERCONNECTING SAID IMPEDANCE MATCHING NETWORKS TO SAID ANTENNA AND FORCHANGING THE TAP CONNECTIONS ON SAID TAPPED SHUNT COIL.